The chemical state of ruthenium in the Ru/MgO and Ru−Cs+/MgO catalysts prepared by the incipient wetness technique with the use of Ru(OH)Cl3 and Cs2CO3 as the catalyst and promoter precursors, respectively, is characterized by X-ray photoelectron spectroscopy (XPS). The influence of the final state effects (the differential charging and variations of the relaxation energy) on the binding energy of Ru 3d5/2 core level measured for supported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parameters determined for the Ru/MgO and Ru−Cs+/MgO catalysts with the corresponding characteristics of polycrystalline Ru foil. High-resolution transmission electron microscopy (HRTEM) in combination with energy dispersive X-ray (EDX) microanalysis reveals that Ru particles in the Ru−Cs+/MgO catalyst are covered with an amorphous layer containing cesium. XPS data show that the layer subjected to the prolonged treatment with H2 at 450 °C consists of cesium suboxide Cs2+ X O. The shift of the Ru 3d5/2 binding energy toward lower values is found for the Ru−Cs+/MgO catalyst (279.7 eV) with respect to metallic Ru (280.2 eV) and the Ru/MgO catalyst (280.5 eV). It is assumed that the shift results from a decrease in the work function of ruthenium under the action of Cs+ cations located on the Ru surface. The data obtained are used to explain the sharp difference in the activities of the Ru/MgO and Ru−Cs+/MgO catalysts for ammonia synthesis at 250−400 °C.

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Citrate is an important stabilizing, reducing, and complexing reagent in the wet chemical synthesis of nanoparticles of silver and other metals, however, the exact nature of adsorbates, and its mechanism of action are still uncertain. Here, we applied X-ray photoelectron spectroscopy, soft X-ray absorption near-edge spectroscopy, and other techniques in order to determine the surface composition and to specify the citrate-related species at Ag nanoparticles 3 immobilized from the dense hydrosol prepared using room-temperature reduction of aqueous Ag + ions with ferrous ions and citrate as stabilizer (Carey Lea method). It was found that, contrary to the common view, the species adsorbed on the Ag nanoparticles are, in large part, products of citrate decomposition comprising an alcohol group and one or two carboxylate bound to the surface Ag, and minor unbound carboxylate group; these may also be mixtures of citrate with lower molecular weight anions. No ketone groups were specified, and very minor surface Ag(I) and Fe (mainly, ferric oxyhydroxides) species were detected. Moreover, the adsorbates were different at AgNPs having various size and shape. The relation between the capping and the particle growth, colloidal stability of the high-concentration sol and properties of AgNPs is briefly considered.